1. Field of the Invention
The present invention generally relates to an air bag device for vehicles. More particularly, the invention relates to an air bag device for vehicles of the type in which an air bag is adapted to be inflated with high-pressure gases, by exploding a squib to thereby trigger a high-pressure gas source, when the vehicle is subjected to an impact (deceleration) of a larger magnitude than a predetermined value, such as due to a collision.
2. Description of Relevant Art
Conventionally, there have been proposed various air bag devices for vehicles, in which, when the vehicle was subjected at a collision thereof to an impact of a larger magnitude than a predetermined value, an air bag disposed in the front part of a passenger room of the vehicle was expanded to be inflated by exploding a squib to trigger a high-pressure gas source, thereby protecting the driver from the impact.
Some of those air bag devices were such that a collision detecting sensor circuit was constituted with a plurality of collision sensors connected in series to each other and each respectively provided with a resistor connected in parallel thereto. The sensor circuit was adapted to be short-circuited by bringing the collision sensors into closed states thereof when, at a collision of the vehicle, the impact thereon is of a magnitude larger than the predetermined value, whereby a short circuit current was conducted across the squib which was connected in series to the sensor circuit, to explode the squib, so that, with high-pressure gases, the air bag was caused to expand to be inflated.
In this respect, in the accompanying drawings, FIG. 2 shows an electrical circuit diagram of a conventional air bag device of such type, which device is designated by reference numeral 100 in FIG. 2. The air bag device 100 included an air bag trigger circuit 105 as a series circuit consisting of an air-bag-oriented fuse 102, a collision sensing circuit 103, and a squib 104, which circuit 105 was connected in series through an ignition switch 107 and a main fuse 120 to a power source 101. The trigger circuit 105 had in parallel therewith a trouble detection circuit 108 connected thereto through a fuse 106. The circuit 108 was adapted to detect for troubles of a pair of collision sensors 110a, 110b (of such a type that is disclosed in U.S. Pat. No. 3,974,350) in the circuit 105. The trouble detection of the collision sensors 110a, 110b by the detection circuit 108 was performed in dependence on variations in the quantity of an electric current flowing between terminals of respective shunt resistors 113a, 113b provided for the collision sensors 110a, 110b. Incidentally, in FIG. 2, designated at reference numeral 109 is an electrical equipment circuit as a circuit of electrical equipment such as a wiper motor, including control switches thereof. This circuit 109 was connected in parallel to the air bag trigger circuit 105 as well as to the trouble detection circuit 108. The collision sensors 110a, 110b were normally open, while the shunt resistors 113a, 113b had resistances of such values that, with an electric current running only through them, the squib 104 could not be exploded. Under the condition that the ignition switch 107 is turned on, the current sent to the squib 104 was conducted from the power source 101 through only the resistors 113a, 113b, thus keeping it from exploding. In this respect, if the vehicle experiences such a collision that produces an impact of a larger magnitude than a predetermined value, the collision sensors 110a, 110b were concurrently operated in a self short circuit manner to short-circuit the collision sensing circuit 103, sending a short circuit current to the squib 104 to explode same, whereby an air bag (not shown) was expanded to be inflated.
With such air bag device, when a vehicle was caused to experience a collision, the driver was effectively protected from the impact thereof.
However, as shown in FIG. 2 also, in such a conventional air bag device, in which an ignition switch as well as a main fuse was interposed as an interruptable element between an electric power source and an air bag trigger circuit, under the condition that the ignition switch is not yet operated to be turned on the trigger circuit was kept from functioning, as a matter of course. Additionally, the ignition switch as once operated might be put in an open state of short duration such as by the chattering thereof, constituting a cause of misfire of a squib.
Moreover, in general, in a vehicle equipped with such an air bag device, the power source consisting of a battery storage was installed beneath the hood of the vehicle while the ignition switch was disposed in the vicinity of a steering wheel. Such a configuration required that a wiring harness connecting the power source to the ignition switch be necessarily rendered relatively long and provided with all the more connections (eg. 120a, 120b, 107a, 107b of FIG. 2), resulting in an enlarged total resistance of wires from the power source to the air bag trigger circuit, as well as an increased possibility of disconnection.
Further, in such air bag device, the ignition switch had at the lower potential side thereof an electrical equipment circuit connected thereto in parallel with the air bag trigger circuit, with the possibility that stable current supply to the trigger circuit might be disturbed by occasional voltage drops due to load effects of associated electrical equipment in service.
In this respect, to decrease such possibility, if the power source was simply directly connected to the air bag trigger circuit, without interposing interruptable elements such as the ignition switch therebetween, then an electric current would have to be always sent to the squib, through shunt resistors connected in parallel to collision sensors, even while the ignition switch is not yet operated, thus resulting in hastened deterioration of the squib. Moreover, for the prevention thereagainst, if an additional relay adapted to close when the ignition switch is operated was connected in series to a collision sensing circuit consisting of the collision sensors and the shunt resistors, then the relay might chatter, with the the fear of occasionally rendering the trigger circuit inoperative.
The present invention has been achieved to effectively solve such problems of conventional air bag devices for vehicles.